This invention relates to continuity and voltage meters and more particularly to a combination tester in which the function of the device is determined by the nature of the circuit to which it is connected.
Prior art believed to be relevant to the present application includes the following U.S. Pat. Nos.: 3,416,074 issued to Schoonover on Dec. 10, 1968; 3,831,089 issued to Pearce on Aug. 20, 1974; 3,872,384 issued to Laass on Mar. 18, 1975; 3,962,630 issued to Chaffee on June 8, 1976; 4,015,201 issued to Chaffee on Mar. 29, 1977; and 4,027,236 issued to Stewart on May 31, 1977. Each of these patents discloses some type of device for measuring voltage in a circuit such as an electrical wiring system in a structure and for checking continuity in such a system. While each of the disclosed devices provides two different functions, they typically require the operation of a mechanical switch in changing from one form of operation to another. In addition, each of the circuits is fairly complicated and involves either solenoid or electronic type relays or solid state amplifiers to perform the various functions. The mechanical moving parts in the switches and solenoids are, of course, subject to failure and the requirement of operating a switch to achieve a particular function always leaves room for error in operating the device. In some cases, failure to switch the device from the continuity test position during a voltage measurement can result in damage to the device.
The above-referenced patents illustrate the usefulness of a device, particularly to commercial electricians, for indicating the voltage present on a given circuit or the state of continuity of the circuit. Such devices are almost essential to the everyday work performed by electrician. It is thefore desirable that such a device be simple, rugged, and reliable.